Mineral wool plant substrate

ABSTRACT

Mineral wool plant substrate formed of a coherent matrix of mineral wool having 99.9 to 75 wt % mineral wool and 0.1 to 25 wt % of an organic substance. Clay may be included in the matrix. The matrix may be in the form of a pellet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mineral wool plant substrate, more inparticular to a mineral wool plant substrate comprising a foreignmaterial in order to improve the properties of the mineral wool plantsubstrate.

2. Description of the Prior Art

Mineral wool plant substrates for plant growth are well-known in the artand consist of a coherent matrix of mineral wool. This coherent matrixis formed by collecting a layer of mineral wool fibres provided with acurable binder, so that after curing the mineral wool fibres aresubstantially not displacable relative to one another. If required forfast uptake of water this coherent matrix of mineral wool may beprovided with a wetting agent.

As mineral wool may be used glass wool, stone wool, rock wool, or slagwool, and/or mixtures thereof.

The fibres may have an average diameter varying in between 1-10 μm. Forrock wool, the fibre diameter is on average about 4 μm.

The density of the coherent matrix of mineral wool may be between 10-200kg/m³, in general in between 30-80 kg/m³.

Such a coherent matrix of mineral wool has a form retaining propertywhich is inherent due to the inorganic starting materials used therein.Furthermore, the water retaining capacity of these mineral wool plantsubstrates is very well controllable and predictable.

A disadvantage may be that during the plant growth, initially the matrixreacts basic so that the pH increases.

It is a desire of growers to alleviate the aforementioned disadvantage,but above that to have the possibility of controlling the exchange ofnutrient cations.

Such properties are inherent to organic substances such as sphagnum andpeat. However, these materials are unsuitable for use in mineral woolplant substrates because during culture they lose structure, and due tobiological degradation of the organic substance, the water retainingcapacity changes such that less air is included within the materialresulting in acidification of the plant substrate.

SUMMARY OF THE INVENTION

The present invention provides a mineral wool plant substrate thatcombines the beneficial properties of both mineral wool and organicsubstances while avoiding substantially the disadvantages of these twomaterials.

According to the present invention is provided a mineral wool plantsubstrate comprising a coherent matrix of mineral wool, with 99.9 to 75wt % mineral wool and 0.1 to 25 wt % organic substance.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes a mineral wool plant substrate comprisinga coherent matrix of mineral wool, with 99.9 to 75 wt % mineral wool and0.1 to 25 wt % organic substance.

By including up to less than 25 wt % organic substance in a coherentmatrix of mineral wool, the degradation of the organic substancesubstantially the structure and the water retaining capacity as well asacidification are avoided. In addition, due to the presence of theorganic substance, the pH decrease is overcome due to the bufferingproperty of the organic substance.

In order to avoid substantially the effect of biological degradation ofthe organic substance it is preferred that the substrate comprises 99.5to 90 wt % mineral wool and 0.5 to 10 wt % organic substance, preferably99.5 to 95 wt % mineral wool and 0.5 to 5 wt % organic substance.

Suitable organic substances are sphagnum and pressed peat assubstantially biological non-degradable organic substances, and peat assuch as a biological degrading organic substance. Using biologicallydegrading organic substances, the mineral wool plant substrate providesfurther advantageous properties linked to the organic substance, namelythe provision of a carbon source. Further, due to the degradation of theorganic substance, growth hormones, humic acids and vitamins arerelaased which are beneficial to plant growth. Chelate forming compoundsare also released which keep slight or insoluble trace elements in thenutrient solution. Accordingly, the plant growth is optimally promoted.

It is emphasized that due to the use of peat the cation exchangecapacity is optimally improved.

When it is desired to provide a mineral wool plant substrate havingproperties in between mineral wool and organic substance, it isworthwhile to partially substitute the organic substance by an inorganicsubstance such as a natural clay. This clay does not provide a carbonsource or growth hormones and chelate compounds but provides anintermediate cation exchange capacity. Accordingly, clay may substitutethe organic substance for up to 99 %, generally for up to 50%,preferably for up to 25%. This means that clay may be present in amountsbetween 0.01 to 9.9 wt %, generally in between 0.2-3%, such as 0.2-1 wt%.

Clay for substitution of the organic substance may comprise soilmaterials comprising hydrophilic particles suitable soil materials havea particle size below 20 ρm, belonging to the class of eroded minerals,such as clays, mixtures of clays with silt and sand having a clayfraction removable as sludge of at least 20%, and further bentonite,kaolin and the like. Particularly suitable are different naturallyoccuring types of clays of mixtures thereof, such as young see clay.Examples are clays comprising 0-100%, preferably 10-50%, most preferablyparticles smaller than 20 μm.

The use of clay provides another advantage when the organic substance isincluded in the matrix in the form of a pellet. Clay functions as alubricating agent and as a material that reduces the compressability ofthe pellet. Accordingly, the amount of clay may be used in order tochange the biodegradable character of the organic substance.Accordingly, peat which is normally biodegradable may be changepartially to substantially nonbiodegradable due to the addition of clayto the pellet. Accordingly, clay may inhibit or retard thebiodegradation of the organic substance. The pellet may have a pelletsize of about 2-10 mm.

Due to the presence of clay and of peat the concentration of sporeelements in the water residing within the mineral wool matrix may becontrolled, due to the sustained release of the cations temporarilystored within the organic substance and/or clay.

Examples of the mineral wool plant substrates according to the inventionare the following.

Coherent matrices of mineral wool are provided having a density of about50 kg/m³ and an average fibre diameter of 4 μm. During the production ofthese plant substrates organic substance in the form of peat is addedduring the formation of the matrix of mineral wool prior to bindercuring. After passing through a curing oven a coherent matrix isobtained.

Plant substrates according to the invention have been preparedcomprising 5, 10 and 20 wt % peate, the remainder being mineral wool.

Other mineral wool plant substrates have been prepared comprising 15 wt% peat, 5 wt % clay and 80 wt % mineral wool.

Another plant substrate made according to the invention comprised 1 wt %sphagnum, 4 wt % clay and 95 wt % mineral wool.

The plant substrates have been used in the growth of plants and haveshown an optimal control of the pH buffering, a sustained release oftrace elements and of the water distribution. During culturing, thebiodegration of peat and sphagnum resulted in a growth of mineralorganisms providing growth promoting compounds to the plants.

What is claimed is:
 1. A mineral wool plant substrate formed of acoherent matrix of mineral wool, consisting of 99.9 to 75 wt % mineralwool and 0.1 to 25 wt % of a mixture of an organic substance and clay,wherein said organic substance is selected from the group consisting ofsphagnum and peat, wherein said clay comprises from 0.1 to 9.9 wt % ofsaid matrix and said clay comprises up to 50 wt % of said mixture, andwherein said matrix has a density of 10 to 200 kg/m³.
 2. The substrate,as claimed in claim 1, wherein said mineral wool is present at 99.5 to90 wt % and said mixture is present at 0.5 TO 10 wt %.
 3. The substrateas claimed in claim 2, wherein the organic substance and the clay areincluded in the matrix in the form of a pellet.